flatlander937's Mazda2 build - SCCA STF / NASA NXF

Hey Zach I double checked the measurements of the shock body stock vs my Koni housing, stock is 13" for the body and my housing is exactly 12". There is roughly 4.5" showing above the top of the tire for stock, so I'll potentially have maybe 3" of usable adjustment(some taken up by the adjuster ring itself). Due to the shorter housing I probably will not be sinking it downwards as it won't gain me anything, it will be mostly all uptravel anyway(which is fine and will be good for ride quality).



In other news: I got my 7in/400lb and 6in/450lb springs:

rJTQZMt.jpg


My solid rod to press into the bearing holders to attempt to prevent welding distortion:

Jy2AEP1.jpg





And I took the time to at least ballpark unsprung weights tonight for shock curve calculation reasons:

oakyMuh.jpg





Here is the pertinent info I found:

According to my bathroom scale:

-My 15x7.5 TRM C1 + 205/50R15 Direzza ZII Star Specs weight 30.8lbs. Note that according to Tirerack wheel and tire weights this combo should be about 30.2lbs. It's mounted, been driven on a bit(so some small pebbles and crap in the tread), and has a valve stem in it so it's not too far off. I just need my unsprung weights estimated somewhat reasonably close.

-The weight of the left front wheel/tire/suspension is 51lbs. This includes the entire weight of the strut, but done properly by disconnecting the sway bar when measuring. Figure about 46lbs since the weight of the top half of the strut plus the whole upper mount is not really unsprung. For other wheel/tire combos it's somewhere in the neighborhood of 13.5lbs + the weight of your wheel/tire combo.

-The rear weight is much more of a pain to estimate because of the trailing beam suspension, you cannot disconnect the "sway bar" and it all gets weighed at once, and some weight is not fully reflected due to me being lazy and not loosening the trailing beam pivot bolts so some bushing compliance probably mucked up the results. Again I just need close enough. With both shocks unbolted and both springs completely removed, the vehicle in the air, I weighed under each tire.

I got 55lbs for the left rear and 57.6lbs for the right rear. As stated above some is clearly lost due to the beam twisting/bushings/etc. This is obvious because with both wheels hanging the weight doesn't add up to the actual weight of two wheels.

To get an idea of how much weight is transmitted across the beam I unbolted the OPPOSITE side wheel/tire to see how it changes the weights. With the left wheel removed, the weight of the right side dropped to 38lbs. I'm estimating there is about 4-5lbs of unsprung weight per side as I measured it, plus the weight of the wheel/tire itself, I'm estimating maybe 2lbs per side due to bushing compliance error, plus maybe another 1lb to account for 1/2 the weight of the shock and spring which were removed for this procedure. So I'm estimating the rear unsprung weight at around 41lbs per side. Most of the weight of the rear trailing beam is located far forward right at the pivot itself, so it has very little effect on unsprung weight as measured at the wheel centerline.



I'll be putting a bunch of info into the suspension calculator on www.farnorthracing.com to try and establish a decent shock curve to know what to order/specify.

Some other ASSumptions I'll be making:

-I did not corner weigh my car. Based on a combination of Edmunds' total weight plus weight distribution measurements(2280lbs 61.9F/38.1R 1411F/869R) plus what Andy Hollis got his down to in full STF prep trim(2188lbs total, 691LF 639RF 370LR 396RR), mine will be somewhere in between. I just need averages of front and rear weights ignoring left and right. I'll be estimating 1380lbs for TOTAL front weight, and 820lbs for TOTAL rear weight. 2200lbs total. The only weight loss efforts I'll really be making will be in losing the battery up front and pulling the spare/tools/etc and running with no gas in the rear. I'm not pulling airbag equipped seats in my daily driver.

edit: Jasyatz has provided some actual corner weights of a car set up basically exactly like mine, so I'll be using his numbers in hopes of it being a little more realistic for calculations.





For those interested, the front motion ratio is somewhere in the .97-.98 neighborhood which is typical of a strut front end. The rear motion ratio is about .97 at the spring, and 1.23 at the shock. I got these as measured from the beam pivot center to the center of the spring is about 14.5in, to center of the "axle" is 15.0in, and to the shock mount is 18.5in.

This means some conversions are necessary to calculate correct shock damping curves(spring and shock are not coaxial with each other). If you were to move the spring from stock location to the shock location(like the Bilstein kit I believe does, or maybe one of the Fiesta kits, I don't keep up with which ones do what), it means your spring is effectively MUCH stronger/heavier now. A 550lb spring on stock perch is the exact same as a 342lb spring in the shock's location due to the different motion ratios. Or said another way a 550lb spring mounted in the SHOCK location is the same as an 884lb spring in the STOCK location.

This is important because in the calculator, you can only enter one motion ratio(it is assumed the same for both spring and shock). So since I want to estimate a 450lb rear spring(in stock location), but want shock forces needed, I will input the motion ratio of the SHOCK where it asks for it, but for the spring rate I will input "280" as that is the equivalent to what would be needed if it were done like a coilover on the shock itself.


I've also estimated the spring ratio of the tires themselves(since the calculator asks for it). I did this by measuring the height of the tires when they are JUST starting to touch the ground(can still spin by hand but starting to drag a bit), the dropping the car with it's normal weight on it, then measuring the height of the tire again with weight on it. I estimated 700lbs on the left front and 400lbs on the left rear. I unfortunately do not have my measurements around me right now, but basically based on applying a "known"(read: estimated) weight, and being able to measure how much it compresses, you can convert the distance measured to a full inch, then based on the multiplier needed to do that, you apply that same number to the "weight applied" and get the spring rate of the tire.


At least in half-ass theory. I just wanted a number. I came up with 1280lbs/in in front and 1072lbs/in in rear. From my limited reading on this subject this is normal because tires increase in spring rate as load is applied. This also means it will be changing constantly while driving so it probably means nothing. It will also change with tire pressure as well. I just wanted a somewhat realistic number estimated to throw into the calculator. +200-400lbs may be more realistic in dynamic loading situations. I'm not an engineer and don't pretend to be, I just want to do all I can to get a suspension that doesn't suck.
 
Last edited:
Edit: messed up the motion ratio conversions initially... Scroll down for the revised charts.
 
Last edited:
Wow! A little too much free time Tony? Great information and a ton of research. It's right where I'm at now with some trial and error. I just went off the Mazdaspeed Bspec kit and adding in a "speculated" rear motion ratio and got to the 550rear spring rate (since the Bspec comes with 450/500) to choose from. I acquired the 600s just in case I wanted to test the upper end of the spectrum.

I think your calculations are close, Even though that's what's in there now, 500 still feels too soft for the front end, I maxed out the shocks yesterday and got the quickest result, best feel and least amount of wheel spin. This is all based on same conditions, same tire pressure as out heat was 6 runs back to back in a 60 minute time frame. (only 35 cars in the heat; 3 heat format). I'm thinking you are dead in with the 34psi tire pressure though. Anything less is just softening the effective front rate and creates a sponginess to mid corner irregularity control...

What did Dennis' calculator come up with for an ideal spring rate? This was my car at baseline at race weight. Same wheels and tires as you, Stock seats, jack tools removed, Injen Intake, flashing E light on fuel, stock exhaust with RB muffler, RB front and rear bars, ALL sway bars still connected and stock battery, and nothing in the car that wasn't bolted down, and before adjustments. Look how close the side weights got, but the corners are a mess.
f668d27fd57e72172632535c80ff7e9e.jpg
That's the scale pic...here's the pic off the app so you don't have to do the math for the corners. Close but needed some love...Final was 50.3 x weight and stayed right around 49.5 side weight but I can't find the final scale pictures. Removing the front bar had the greatest impact on corner weight, adjustable links were needed, but I just disconnected the bar and am running with the RB front bar not connected now..
712fa2bedea141dbec99f8c87afe03ac.jpg


Great stuff...we'll get there soon enough. NJ Pro is in 4 weeks, I'll put as much of your science to use as I can and see how well it works...Granted not as much shock control, but I think I'm close to your curves.

---note if you read this post over the last 30min, you'll see that the text changed a few times. I'm a horrible picture folder storer and whence I crossed the date/time on the pictures with the Phone notes, I was able to get the correct information above. Turns out I gave Rich (Extreme's) everything on his car, and have nothing else on mine since my old phone exploded and I only backed up certain pics. Rich's car which was very very close to an STF minimal build came in around 2140lbs no driver with a few tricks, weight could be minimized by another 50lbs..
 
Last edited:
Thanks for those weights! Basically exactly how my car will sit so I ran the numbers again with those weights:


550/450 = 2.4/2.9hz


As per the calculator, roughly 600/365 is ideal at 2.5/2.7hz


Still waiting to hear back from Dennis Grant. I suspect high rear rates is a normal FWD thing.

edit: Corrected some numbers, originally did not square the motion ratios so was getting an artificially high ride frequency for the rear.
 
Last edited:
I'm 50less in front and 100more in rear from your calculated, and a ton more rear than "ideal". Is that where you've settled? And for a "a hundred years" it's been "normal" to run higher rear spring rates on a FWD car. But that's been the rule with the IRS rears. This twist beam stuff is from the 80s and most of that paper that notes were taken on back then burned.

Funny though the rear rate on the Bilstein Autox kit was right near ideal and the jury is still out on to whether that was enough. I have my opinions and now I'm not sure. I can tell you the car rides a ton better with the 500/550s than it ever did with the Bilstein kit.

My first car was a Dodge Charger, not the good kind, the K car variant. seems I'm a bit attached to the 80s..
 
Last edited:
Yeah I just want to establish a baseline. And I'm thinking out loud(via keyboard). I suspect 550/500 will end up about right ride frequencies be damned.


And I like the k-cars, had 2 Sundances, one was 2.5 T1 car.
 
It came to my attention that when comparing or adjusting for motion ratios, you need to square the motion ratio when converting to/from wheel rates(Thanks to Zach)... so I'll be editing the previous post to reflect that.

Basically a 550/450 spring combo must be entered in as 550/280. 280lbs at the shock is same as 450lbs at spring perch.

450*(.97^2)

450*.941

= 423.45 wheel rate

423.45/(1.23^2)

423.45/1.513

= 279.87lb spring at the shock.

So whatever spring you're thinking about running you must convert into lbs at the shock(as if it were mounted coaxially w/ shock) so that the calculator spits out the correct ride frequencies and shock information..

FWIW with 550/450 springs you end up with 2.4 and 2.9hz ride frequencies. 600/450 = 2.5/2.9hz.
 
And here are the calculator screenshots with updated information:

jmGiBh0.jpg


27v0pIH.jpg



So I want some shocks that have about 15lbs of force in compression at 2in/sec, and 30lbs of force in rebound at 2in/sec.

Koni specs their 30 series circle track shocks out at multiple speeds, 2in/sec is one of them. Unfortunately this confirms that all of their shocks available are either too heavy in compression or too heavy in rebound, by a LOT. Most of their stuff is also inverted where compression is more force than rebound due to roundy round setup dictating that.

So it looks like custom valved Bilsteins will be the way to go. I have been trying to research what their off the shelf valving for their circle track shocks mean... but every line of shock has a different rating system. From reading some circle track boards it seems like the ones that have double two-digit valving numbers(40-20 or 70-45) converts to other shock ratings of the normal single digit numbers(4-2 and 7-4.5 respectively)... and this "industry standard" is spec'd out at 3in/sec... meaning the 40-20 valving MAY be reasonably close.... but that doesn't tell you anything about the rest of the dyno graph(how much high speed or low speed damping it has). It could well be retarded-stiff like the Koni 30 series or floaty when hitting large bumps.
 
Trust me, get more compression...Every FWD shock I've ever owned and revalved I've gotten more compression added, especially if it's adjustable. Worse case you can adjust the compressions down to the rebound level you like. Bilsteins are nice and cheap to revalve but whence you get into adjustable types, very pricey. Konis whence opened and revalved by human hands (as opposed to factory built) are very temperamental and tend to leak or go dead after just a few years. Bilsteins are lifetime shocks if rebuilt by Bilstein themselves. Koni service is fantastic though, you can get a hold of those guys very easy and Lee Grimes is a top notch resource and bends over backwards for racers. Bilstein is "leave a message" and we'll call you. Their revalve process is mail it in, and we'll call you when we get to your stuff. Bilstein for their non adjustable stuff is $75-$125 per corner; Koni is $175-$299 each for doubles.

Tough decisions, but try to see if you can get something OTS in either brand, even if it's not ideal but close. You'll get a longer service life out of it and have less cost to boot.
 
Another question. Do you want to get ideal spring rates in your setup sheet with the driver in it? I'll keep looking around for final values of my car with driver. Worse comes to worse, I can rescale it soon. just need to run over to my buddy's house and grab them..
 
I couldn't find the scale pics, but here's the shock compare pics we spoke of on FB
1e3638d1d2a0789e1ac76f0ed165408c.jpg
0a7e889da57f13c3fa542ded115a2f3b.jpg
ad51951da14e338a756ded6534f0b109.jpg


Borrowed from Extremes31 build thread.

Focus SVT KYB to Bilstein non adjustable Autox kit rears
1d5506432ea36c1ae0b477e5b8e6159b.jpg
 
Last edited:
Another question. Do you want to get ideal spring rates in your setup sheet with the driver in it? I'll keep looking around for final values of my car with driver. Worse comes to worse, I can rescale it soon. just need to run over to my buddy's house and grab them..

That's OK, I'm just looking for close enough to get it going, I plan on corner weighting when all together and rates feel right.

And thanks for the shock pics!


I do think a Koni 30-7325 may be close enough to work. I think only the lowest rebound setting will be useful though.

Or Koni 30-8414. Bit more compression, more usable rebound for daily driving on low settings, high setting probably right for auto-x. Not available in 7in stroke so 8 would work too.

Force Chart for 30-series shocks
http://www.koniracing.com/images/File/30force.pdf
 
Last edited:
Have you looked into the Koni doubles from a Fox body mustang rear? They fit in the car, just not sure what the valve curve looks like. They are sold OTS And widely available.
 
I've not, there is a dyno chart posted of the koni singles and doubles on Corner Carvers for read of a Fox Mustang but I'm not a member, and they require a paid email address to join. Gmail and Yahoo are not accepted.
 
FWIW I just called Lee Grimes at Koni NA, super nice guy. I gave him some info to pass onto someone else there to look into viable applications for 450-550lb rear springs. Jeff I gave him your corner weights so this could help you too :p Lee said the Koni 30-7325 sounds like a really good starting point off the top of his head. Also they can have the valving modified and converted to double adjustable for a fee(unsure of exact amount but I'll guess $200+ ea) down the road if desired.
 
The 30 series are monotube as well which is a nice plus.

I am also hoping to have my new setup complete this weekend, at least for a test drive. I will then take it apart again to get the housings powdercoated. I will have some pictures in my build thread as well.
 
The 30 series are monotube as well which is a nice plus.

I am also hoping to have my new setup complete this weekend, at least for a test drive. I will then take it apart again to get the housings powdercoated. I will have some pictures in my build thread as well.

Yeah that is nice! I'm anxious to see how your setup turns out, what are you running for rears again?


I called Stuart Maxcy as well this morning. It looks like I'd be out $500 for SN shocks + valving, or $260 for the Koni 30 series. I'm waiting to see what Gordon at Koni thinks. Granted I think the Bilsteins are the superior damper in the end. At this point another $200 is nothing, and revalving/rebuilding down the road will save $.
 
400lbs/in springs and koni yellows from a focus. I think I had the rear valving a little stiffer than really needed in the rear just to make up for the lack of dampening on the front bilstiens when I raised the spring rate. Thats why I am really looking forward to what the fronts will ride like with yellows in the front.
 
The Focus yellows were another one I was considering trying.

Anyway I just pulled the trigger on some 7in travel Bilstein SN take-apart shocks. The wife told me to buy what I need once. (laugh)

When they show up I'll do some mock up to make new upper mounts to get the proper up/down travel before I send them to Stuart at Maxcy Speed & Co in Texas for valving.
 
So after a couple days of screwing around I find out that the Bilsteins I want are backordered with no known ETA(could be next week, could be 2 months from now). There are a few places with them in stock, for $190+... but the idea was to try and save some money going with Coleman Racing.

Anyway I called Lee Grimes at Koni NA and he checked with one of their Motorsport Engineers and they agreed that the normal Koni Sport rear shocks should be able to handle 450-500lb springs without any real issues. They can always be revalved if really needed(albeit it's $$$ unless I go to Lincoln for the Solo Nationals, where they revalve shocks for free if you're a driver, just pay for parts).

I am still interested in learning to valve stuff myself, so I may eventually get some Bilsteins to screw around with next year/winter just for grins.







Also for the last week I have had a misfire occuring at first only barely noticeably at idle. It progressed to happening more pronounced, again only at idle maybe under very light load while moving in parking lots, etc. I was nervous as this is how Mini Coopers and some other German cars act when the exhaust valves get burnt and then you're screwed and need to pull the head. No codes were being set but you could definitely feel it.

Fast forward to today, I decided to seafoam it for grins in the event it's from carbon on the valves. Wouldn't hurt right? Made it worse, started misfiring much more noticeably/consistently... but this made it a good thing since now driving it for 10min would result in a misfire code being set(P0301, cyl 1 misfire).

Swapped coils 1 and 2, inspected plug #1, looked OK, gap just a bit big at 0.048 but should be fine... still misfiring on 1. I was more nervous now about it being a burnt valve. It's under powertrain warranty for a little while longer but the local Mazda dealer is kind of awful.

It couldn't possibly be the plugs right? Iridiums are fine for 75k miles as per Mazda. I've never seen a plug fail so early in it's life(at 50k) so I was kind of doubting it but whatever, I got some NGK replacements(Iridium BKR5EIX-11), also swapped injectors 1 and 3 while I had the stupid air box off in the event the misfire was still present. If it moves then it would mean injector failure. I also did a compression test while all the plugs were out and while the engine was still hot(since that's when misfires are the worst).

Compression results were 185-190-190-185... whew! Made me feel a bit better.

So I got it all back together and it is back to running well again! I guess our ignition systems are kind of weak... old plugs were worn to about 0.048", spec is 0.042" IIRC. In my experience that isn't worn too terribly much, I wouldn't expect it to cause problems, but that was the issue apparently. Normally when plugs are worn you'd expect misfires among multiple cylinders, or a P0300 code, etc. It was just a weird onset of symptoms that had me freaking out a little bit.
 
Back